1. Field of the Present Invention
The present invention generally relates to a semiconductor device for performing fingerprint recognition, and particularly relates to a semiconductor device for performing fingerprint recognition by tracing a fingerprint provided by a finger to a recognition area of the semiconductor device for fingerprint recognition.
In recent years, portable apparatuses have become capable of providing high performances. Especially, portable telephones are capable of storing a large volume of personal information with increases in storage capacity, and it is universally required that the personal information not be perused by persons other than owners.
Also, systems that perform electronic banking by using a portable telephone as a terminal are available. With these developments, a fingerprint sensor that is an authentication device using the fingerprint attracts attention.
In these applications, the semiconductor device for fingerprint recognition is required to perform fingerprint recognition with high reliability.
2. Description of the Related Art
Conventionally, there are an optical detecting method and an electrostatic-capacity detecting method for fingerprint detection using a fingerprint collating system. Of these, the electrostatic-capacity detecting method is the method of detecting an electrostatic-capacity value between a finger and an electrode formed in a fingerprint detection area of a semiconductor device for fingerprint recognition. Since a semiconductor device for fingerprint recognition using the electrostatic-capacity detecting method can be easily miniaturized, such applications in small electronic apparatuses and the like are advancing.
Since the semiconductor device for fingerprint recognition of the electrostatic-capacity detecting method requires a finger to contact the electrode and to sweep in a direction, the fingerprint detection area of the semiconductor device is exposed. For this reason, the structure is such that an opening is formed in a sealing resin that encloses the semiconductor device, and the fingerprint detection area is exposed to the outside through the opening.
Further, as a packaging structure of the semiconductor device for fingerprint recognition, packaging structures used by common semiconductor devices are used, for example, a BGA (Ball Grid Array) type packaging structure is often used.
FIG. 1 shows an example of this kind of semiconductor device for fingerprint recognition (henceforth a fingerprint sensor). In essence, a fingerprint sensor 1 includes a semiconductor chip 2, a substrate 3, and a sealing resin 4.
A fingerprint recognition area (henceforth a sensor unit 6) for fingerprint recognition is formed on a circuit formation side (upper surface according to FIG. 1) of the semiconductor chip 2. As a finger sweeps across the upper part of the sensor unit 6, the semiconductor chip 2 detects the electrostatic-capacity value between the finger and the sensor unit 6, and detects the fingerprint.
The substrate 3 is a glass epoxy substrate, and is structured such that a wiring layer is formed on both upper and lower sides of a glass epoxy insulation material. The semiconductor chip 2 is fixed to the substrate 3 by a die bonding material 8.
At this instance, the rear side (i.e., the side opposite to the side on which the sensor unit 6 is formed, namely, the bottom surface) of the semiconductor chip 2 is fixed to the substrate 3 so that the sensor unit 6 is exposed to the outside for a finger to sweep across. Further, a golden wire 7 electrically connects the semiconductor chip 2 to the substrate 3.
The sealing resin 4 is formed such that the semiconductor chip 2 and the golden wire 7 are covered, and thus protected. In order for the sensor unit 6 to be exposed for being swept by the finger, an opening 9 is formed in the sealing resin 4 at the position that corresponds to the sensor unit 6. In this manner, even if the sealing resin 4 is formed, the finger can touch the sensor unit 6 (refer to, for example, JP, 9-289268, A (page 6, FIG. 11)).
FIG. 2 shows how the sealing resin 4 is formed. As mentioned above, it is necessary to form the opening 9 in the sealing resin 4 at the position that corresponds to the sensor unit 6. For this reason, in a conventional practice, a molding metal 10 is prepared with a spacer 11 so that the sensor unit 6 is covered as illustrated.
The spacer 11 is formed of a flexible material, such as plastic, and when clamping the molding metal 10 for forming the sealing resin 4, the spacer 11 closely adheres to the sensor unit 6 such that the sealing resin 4 is prevented from flowing into the sensor unit 6.
According to the conventional fingerprint sensor 1, there is a possibility that the resin can leak from a minute crevice between the semiconductor chip 2 and the spacer 11 when forming the sealing resin 4. If the resin leaks, the resin starts covering the sensor unit 6 as shown in FIG. 3 (such leaking resin is called resin flash 12). When the resin flash 12 is generated on the surface of the sensor unit 6, there is a problem in that the semiconductor chip 2 cannot properly operate, and accurate fingerprint recognition becomes impossible.
Further, when forming the sealing resin 4, the spacer 11 directly contacts the sensor unit 6, and the spacer 11 is pressed by the molding metal 10 to the semiconductor chip 2. Although the spacer 11 is made of a flexible material, such as plastic, it is well known that great clamping force is applied when clamping the molding metal 10. For this reason, according to the conventional practice, wherein the spacer 11 directly contacts the sensor unit 6, there is an additional problem in that the sensor unit 6 and the semiconductor chip 2 may receive damage such as a crack and the like, causing the reliability to be degraded.